The present invention relates generally to insect control and more particularly to passive insect control articles that are effective in killing or repelling mosquitoes.
For certain applications, it is important to be able to control flying insects for six to ten hour or even longer periods within defined areas such as the enclosed space of a bedroom. Such a duration of insect control is desirable, for example, to protect a sleeper occupying an unscreened room from mosquitoes for a single night. It is also useful to be able to deliver an insect controlling amount of active ingredient nightly for multiple nights in succession. Successful flying insect control is also useful in other living spaces, including screened areas that for any reason are still subject to invasion by flying insects, as well as outdoor areas such as a patio, or the like.
Traditionally, articles or devices that dispense insecticide vapors to control insects in such settings require heating or burning a liquid or solid substrate to evaporate the active ingredients. For example, conventional citronella candles have long been used for such purposes. Burning insect coils are also commonly used to achieve a night""s insect control or to control mosquitoes or other insects in outdoor areas. The product sold by S. C. Johnson and Son, Inc. of Racine, Wis. under the trademark xe2x80x9c45 Nightsxe2x80x9d is an example of a type of product known in the art for delivering insect control over repeated periods of use, such as a nightly use in an unscreened bedroom. The xe2x80x9c45 Nightsxe2x80x9d product is an example of conventional heated, liquid evaporation insect control products.
The products referred to above all can be effective, within certain limits. However, products that require a heat source also require a safe burning site, e.g. in the case of insect coils, or may require a source of house electrical current for typical heated evaporation products. Products exist that are designed to avoid some of these difficulties by employing passive evaporation of insect control active ingredients without the application of heat. However, they have problems and limitations when compared to insect control strategies employing products requiring the application of heat.
For example, Regan, U.S. Pat. No. 339,810 uses a tobacco preparation as a repellent that is first soaked into cloth or paper and then dried. The repellent active ingredient is reported to evaporate from the substrate to repel insects. More recent technology such as that disclosed in Landsman et al, U.S. Pat. No. 3,295,246 has included the use of pyrethrum or pyrethroid materials as passively evaporated insect control active ingredients. Ensing, U.S. Pat. No. 4,178,384 employs pyrethroids as repellents applied to the locus to be protected.
Whitcomb, U.S. Pat. No. 4,130,450 describes an insecticide-impregnated, open, low-density web that provides an expanded surface that may be loaded with contact insecticides, including pyrethrum and synthetically prepared insecticides. Whitcomb prefers the use of micro-encapsulated pyrethrum to avoid pyrethrum instability when exposed to ultraviolet light and oxygen. Whitcomb mentions that the web may be hung to permit vaporization of the active ingredient to combat flies. Similarly, Chadwick et al, U.S. Pat. No. 5,229,122 utilizes a mixture of micro-encapsulated and non-micro-encapsulated active ingredients, noting that any known pesticide may be used for the purpose. Pyrethrunim or a pyrethroid equivalent are referred to as possible pesticides. The preparation is used to coat surfaces, although it is also noted that the vapor phase of the pesticides may be valuable.
Kauth et al, U.S. Pat. No. 4,796,381, is an example of the use of paper or textile strips impregnated with insecticide that is allowed to evaporate to control insect pests. The Kauth et al materials utilize pyrethroids and, in particular, vaporthrin, permethrin, and bioallethrin. However, the devices of Kauth et al are designed to be hung in closets or placed in drawers, suggesting that they are understood to be inadequate to protect larger, more open spaces. Nothing in Kauth et al suggests any ability of their paper or textile strips to control insects in relatively large air spaces.
Samson et al, U.S. Pat. Nos. 5,198,287 and 5,252,387 disclose a fabric for use in a tent, the fabric including a coating that contains evaporable insecticides, and in particular, permethrin. Again, a confined space is being protected.
Aki et al, U.S. Pat. No. 4,966,796, utilizes a pyrethroid insecticide on kraft paper, with additional layers of untreated kraft paper added to create a material useful for making an insect-resistive packaging material or bag.
Landsman et al U.S. Pat. No. 3,295,246 teaches the use of an insecticide-soaked and then dried paper that is coated with resin to slow evaporation of the active ingredient. The resin coating is deemed important to make an insecticide product that will be effective over a long period of time. Example formulations cited in Landsman et al include pyrethrins as active ingredients. The Landsman et al product is not intended to protect large volumes of air and is also an example of the difficulty known in the art of achieving protection over an extended period of time because of the evaporative rate of active ingredients.
Ronning et al, U.S. Pat. No. 4,765,982 is an example of the use of micro encapsulated active ingredients to achieve a sustained release insect control effect. Pyrethroids, either synthetic or xe2x80x9cnatural,xe2x80x9d are cited as useful. The Ronning et al insecticidal device may be hung in the open to achieve a repellent effect in a restricted locale to drive insects from a nest or the like.
Yano et al, U.S. Pat. No. 5,091,183 and Matthewson, U.S. Pat. Nos. 4,940,729 and 5,290,774 cite specific insecticidal compounds for volatilization. Yano et al specifically discusses the use of impregnated papers for heatless evaporation of an insecticidal compound.
Clarke, U.S. Pat. No. 2,720,013, describes the use of a fabric material into which active ingredients are pressed or fused. Pyrethrum is cited as useful not by itself but as at least one element in a mixture of insecticides. The Clarke fabric material is designed to be adhered to the blades of an electric fan so that the insecticide will be directed into the area ventilated by the fan.
Emmrich et al WO96/32843 describes an insect control article to control flying insects comprising a substrate that is impregnated with an active insect control ingredient available for passive evaporation, wherein the active insect control ingredient is selected from transfluthrin, prallethrin, vapothrin, tefluthrin, esbiothrin, dichlovos (DDVP), and combinations thereof. Emmrich et al teaches that the insect control article must then be placed in an environment with significant air currents in such a manner that the substrate of the insect control article is exposed to the air currents, and the active insect control ingredient impregnated within the substrate is allowed to evaporate passively into the air. These air currents are referred to as xe2x80x9csignificantxe2x80x9d since they are caused by either augmenting air movement via a fan, blower, etc. or the air movement is non-augmented but has a relatively strong natural air current such as that occurring when wind blows through an open window or door. Emmrich et al""s insect control article does not require any external heat be applied to the article to vaporize the active ingredient although heat will, of course, aid in the rate of evaporation of the active from the substrate.
Another device not requiring heat but requiring a relatively strong augmented air current is taught by Ito in EP0775441. This device includes a carrier supporting a substrate containing a pesticide that is hard to vaporize at normal temperatures, and a blower for developing an air current across the substrate.
As seen from the above prior art, although passive evaporation of insecticides is known in the art, the nature of those materials has been such that the attention of the art generally has been directed to their application to closely restricted spaces or to the area in the immediate vicinity of the materials or to methods of use requiring fans, significant air currents or the like. Within that context, the art has focused on the need to provide for artificially extending the longevity of insect control by use of a slow release structure or regimen of some sort, or the like. Heat or augmented air movement and not passive evaporation have been the predominant means to achieve practical distribution of insecticide throughout a large volume of air, and heated evaporation from a liquid reservoir has been the practical means of achieving protection over a multiplicity of days.
As discussed above, currently available insect space repellent products typically require heat to drive the active into the ambient (e.g., coils, electric mats, liquid vaporizers, and citronella candles). These products demand either electric energy or chemical energy to vaporize the relatively low volatile actives. Products that run on electric energy cannot be used effectively in regions where there is scarcity of power supply. In addition, since such products are relatively expensive to consumers in such regions, less expensive insecticidal coils are typically used in these areas. However, excessive smoke, a burning tip, and residual ash are undesirable. A low-cost passive type of product, which requires no electricity or battery for heating, has no burning tip or residual ash, and does not release smoke would be most suitable for this segment of the market. However, as previously noted herein, a major problem with such passive insect control articles has been insufficient release rates due to low volatility of the actives and their substantial solubility in the substrate which limits the use of commercially available products based on passive evaporation technology to small enclosures such as closets or to arrangements which require augmented air movement to increase the release rate of the active.
Theoretically, any insecticide active when applied on any surface can be made to effectively control insects if sufficiently large quantity of the active is applied over a relatively large macro surface area. This technology becomes impractical and cost prohibitive under such circumstances because typically, a large amount of insecticide is absorbed or solubilized and entrapped into the substrate and only a portion of it is readily released into the air. Furthermore, the substrate needs to be very large which adds to the cost. This theoretical knowledge therefore cannot be put to practical commercial use. The present discovery specifically relates to making the passive evaporation technology work effectively at very low dose levels distributed over reasonable areas. For this, it is not only necessary to choose the right active, but also the right substrate and a right solvent. The right active is the one that is most effective against flying insects at low concentrations and has sufficient volatility to attain these concentrations. The right substrate is the one which provides the least resistance to the diffusion of active into the ambient. The right solvent is the one which solubilizes the active, distributes the active on the surface of the substrate uniformly, does not attack the substrate, and volatilizes itself rapidly without substantially volatilizing the active itself.
The insect control article of the present invention to control flying insects essentially comprises a non-absorbing and inert substrate coated with an active insect control ingredient that is available for passive evaporation. The active insect control ingredient is selected from the group consisting of transfluthrin, tefluthrin, and combinations thereof. Preferably, the active insect control ingredient includes at least one of transfluthrin and tefluthrin, and most preferably the active control ingredient includes at least transfluthrin.
When an active is absorbed or solubilized in the substrate, passive evaporation becomes substantially difficult due to additional mass transfer resistances encountered due to the substrate. However, if the solubility of the active is lower than 40 micrograms per square centimeter of the substrate, and preferably less than or equal to about 20 xcexcg/cm2, during practical applications, the active predominantly resides on the surface of the substrate and hence is readily available for evaporation. The substrate in this case does not provide any additional significant resistance to diffusion of the active into the environment. This particular substrate characteristic also enables the active to volatilize most uniformly until all the active evaporates from the surface of the substrate. Otherwise, typically, an absorbing substrate or a substrate with high solubility of active (or a substrate with both these characteristics) would release the active only partially, and in addition, in a non-uniform fashion.
The method of the invention for controlling flying insects includes the initial step of providing an insect control article having a non-absorbing and inert substrate that is coated with an active insect control ingredient available for passive evaporation, wherein the active insect control ingredient is selected from the group consisting of transfluthrin, tefluthrin, and combinations thereof. Preferably, the active insect control ingredient includes at least one of transfluthrin and tefluthrin, and most preferably the active control ingredient includes at least transfluthrin. Preferably the active is applied by means of a carrier solvent with low Hansen""s hydrogen bonding parameter. The insect control article is then placed in an environment such as a bedroom in such a manner that the substrate of the insect control article is exposed to non-augmented air movements. The active insect control ingredient coated on the substrate then is allowed to evaporate passively into the air without the aid of a mechanical device such as heater or fan, preferably at a release rate of at least 0.2 mg/hr for any desirable duration.
Transfluthrin (also called Bayothrin or NAK 4455) has high potency against mosquitoes, flies, cockroaches, and moths. The chemical name of transfluthrin is (IR-trans)-(2,3,5,6-tetrafluorophenyl)methyl 3-(2,2-dichoroethenyl)-2,2-dimethyl cyclopropane carboxylate. Its extremely rapid knock-down property, even at very low concentrations and application rates, makes this chemical particularly suitable for passive evaporation technology. Unlike the prior art, passive evaporation technology in accordance with the present invention effectively controls flying insects even though it only utilizes non-augmented or insignificant natural air movements and diffusion as a means of releasing effective levels of active to provide the desirable repellency effect. The present invention provides the appropriate combination of substrate, solvent, and coating density that gives optimal efficacy at minimal cost. Specifically, the present invention teaches (a) that some materials are better than others for use as the substrate due to their physical and chemical resistance to the active, (b) that non-absorbing substrates release active more uniformly than absorbing substrates, (c) that carrier solvents with low Hansen hydrogen bonding and dispersive parameters and low volatility improve repellent strip efficacy, and (d) that biological efficacy remains substantially constant over time when the coating density lies in a certain range.